Goldfish come in many shapes and sizes and thus so do the RULES regarding maintaining them. Goldfish should never be kept in a bowl under any circumstance. A single fancy
goldfish should have 15g of overly filtered water. A comet goldfish will grow, in the aquarium, up to 8 inches long and up to 12-15 inches long in a pond. So a bowl is certainly no place for these little beings.
A filter should be properly installed to ensure no bad bacteria results. Good bacteria needs to survive in the tank, and this requires the pump to be kept on at all times. Gravel is not entirely necessary, and in all honesty, can make clean up a true MESS. Some fish owners believe that other water ‘cleaners’ may help with tank waste (such as snails/algae/etc), but in all honesty, these little ‘cleaners’ actually end up making more of a mess. Keep it simple for the sake of your fish!